There exist infrared detectors comprised of semiconductor materials. An example of such an infrared detector has a configuration where an infrared absorption layer with an InAs/GaSb superlattice structure is formed on a GaSb substrate. The InAs/GaSb superlattice structure forming the infrared absorption layer is a type-II superlattice (T2SL) structure and has a type-II band lineup. Accordingly, by adjusting the film thickness and the period of the superlattice of the InAs/GaSb superlattice structure, it is possible to obtain an infrared detector that is sensitive in a wavelength range from a middle wave (MW) infrared wavelength of 3-5 μm to a long wave (LW) infrared wavelength of 8-10 μm.
A PIN-type infrared detector with a T2SL structure uses interband optical absorption. For this reason, it is expected that a PIN-type infrared detector with a T2SL structure will have improved temperature characteristics compared with a quantum dot infrared photodetector (QDIP) and a quantum well infrared photodetector (QWIP) that use intersubband optical absorption. Such a PIN-type infrared detector with a T2SL structure is desired to have high light sensitivity and a low dark current in addition to improved temperature characteristics.
To obtain a PIN-type infrared detector using a T2SL structure and having high light sensitivity and a low dark current, it is necessary to form a high-quality T2SL crystal in the infrared absorption layer. Also, to form a high-quality T2SL crystal, it is necessary to form a GaSb buffer layer with high flatness below the infrared absorption layer (see, for example, Japanese Laid-Open Patent Publication No. 2015-109388 and Japanese Laid-Open Patent Publication No. 03-129721). For example, “M. Lee et al., Journal of Applied Physics 59, 2895 (1986)” proposes improving the quality of a GaSb buffer layer by changing the growth temperature and the V/III ratio in molecular beam epitaxy (MBE). Specifically, “M. Lee et al., Journal of Applied Physics 59, 2895 (1986)” discloses that an excellent GaSb layer can be formed by performing epitaxial growth at a growth temperature between 500° C. and 550° C. and with a V/III ratio between 5 and 10.